A core facility is operative in this laboratory for the production and maintenance monoclonal antibodies. The core is situated in a separate room equipped with laminar flow hoods, incubators, centrifuge, refrigerators, ELISA reader, and scintillation counters. The core provides the following services that are used by all program participants: 1) Assistance with the development of new monoclonal antibodies. 2) Maintenance of a large stock of cell lines and hybridomas. 3) Production of monoclonals as titred ascites and culture supernatants, purified immunoglobulin fractions, and modified Ig's (Fab fragments and biotin or fluorescein-Ig's). 4) Production of polyclonal (rabbit) antisera. 5) Mycoplasma screens and recloning of cell lines. 6) Assistance with ELISA assays and radioimmune assays.